Method of flameproofing a cellulosic textile



United States Patent 3,253,881 METHOD OF FLAMEPROQFING A CELLULOSTC TEXTHLE Edwin L. Donahue, 185 Pasadena Place, Hawthorne, N.J.; Marguerite S. Donahue, executrix of said Edwin L. Donahue, deceased No Drawing. Filed June 14, 1962, Ser. No. 202,405 4 filaims. (Cl. 8-1162) This application is a continuation-in-part of my prior application, Serial No. 763,444, filed September 26, 1958, now abandoned.

This invention relates to a novel composition and method for flameproofing cellulosic material. More particularly the invention concerns the flameproofing of cellulosic textiles with urea-phosphoric acid type flameproofing agents in the presence of pyridine and its derivatives.

The flameproofing of cellulosic materials, such as cotton or rayon fabrics, has assumed increased importance by reason of the extensive adoption of clothing and other articles made from such materials in military operations and the need to protect them from the effects of thermal and nuclear radiations. It is also of importance that the treated fabrics be capable of being washed and drycleaned many times with no loss of their fiameproofing properties.

It has been known for many years that the treatment of cotton fabrics with mixtures of urea and phosphoric acid accompanied by curing at elevated temperatures imparts to the fabric a fiameproof finish which is resistant to hot water Washing and mild soap scouring. Workers in this field have ascribed the flameproofing effect to surface esterification of the cellulose with possible formation of an ammonium salt of cellulosephosphoric acid.

Conventionally, the urea-phosphoric acid reaction is carried out by immersing a cellulosic fabric in an aqueous solution of urea and orthophosphoric acid, squeezing out the excess solution, drying at about 200 to 250 F. and then curing the fabric for about 3 to 20 minutes at a temperature between about 260 and about 400 F. The curing time depends upon the temperature employed, the composition of the treating bath, and the type of cellulose material, but excessive curing is to be avoided since it results in reduced tear and tensile strengths.

The ratio of urea to phosphoric acid is not critical, but generally ranges from about 2 to 6 mols of urea per mol of acid. Care must be taken to avoid degradation of the cellulose by controlling the acidity. It has been proposed in the prior art to add a volatile alkaline agent such as ammonium hydroxide to adjust the pH value to a favorable range, namely from about 6 to 8. However, fairly large quantities of ammonium hydroxide must be used, and its volatility is such that formaldehyde needs to be added to control loss of ammonia, and this increases the time required for curing.

It is also known to react the urea and phosphoric acid with the cellulosic material under conditions such that the urea remains molten throughout the reaction, or else to react the urea and the phosphoric acid by melting them together, cooling and then adding water to make the required solution. It has also been proposed to employ other nitrogenous materials wholly or partly as substitutes for the urea, such as guanidine, biuret, dicyandiamide, and the like.

6 One of the principal objectives of prior art methods,

and one which is also an object of the present invention, is the production of a fiameproofed material wherein the character of the fiameproofing is such that it is durable. By this it is meant that it will not change the normal appearance of the fabric, nor its normal wearing qualities, but especially that it is resistant to the action 3,253,831 Patented May 31, 1966 of water in liquid or vapor form, and to soap solutions, detergents, and dry-cleaning solvents, without loss or impairment of flameproof proper-ties. These qualities are especially important where the treated fabric must meet military specifications.

In accordance with the invention there is provided a novel flameproofing composition for application to cellulosic materials comprising an organic nitrogen base, an acid of phosphorus, and a small amount of a heterocyclic nitrogen base or a derivative thereof. The organic nitrogen base and the acid of phosphorus react to form a fiameproofing composition of the urea-phosphoric acid type. The heterocyclic nitrogen base functions primarily as a catalyst, promoting esterification of the cellulose. The heterocyclic nitrogen base may also be employed, however, in the form of a derivative which possesses surface activity, and in such case it has been found to promote retention of the flameproof properties of the fabric and to exhibit a mordant-like action in promoting fastness and retention of the dye on the fabric in the case of colored fabrics.

The organic base which is employed as a reactant in accordance with the invention may be an amide or an amine, such as, for example, urea, melamine, guanidine, dicyandiamide, and the like. Where the free base is used, urea is preferred, The base may also be employed in the form of a nitrogenous condensation product, such as, for example, a monomeric reaction product of urea and formaldehyde (methylol-urea), or a polymeric re action product of urea and formaldehyde. Furthermore, there may be employed mixtures of various amines or amides with each other and/or with their resinous reaction products.

In general, there is utilized an excess of base, ranging from about 2 to 6 mols per mol of the acid of phosphorus in order to raise the pH of the composition so that when applied to the fabric there will result in the fabric a pH in the range of about 5.4 to about 6.3, which has been found to yield favorable results.

The preferred acid of phosphorus is orthophosphoric acid (P1 1 0 which is advantageously employed in the commercial or strengths. However, there may also be used metaphosphoric, pyrophosphoric, orthophosphorous, pyrophosphorous, or polyphosphoric acids.

In accordance with the invention there is included in the urea-phosphoric acid type fiameproofing bath a small amount of a heterocyclic nitrogen base or a derivative thereof. Examples of such heterocyclic nitrogen bases include pyridine and quinoline, but pyridine is preferred owing to its lower cost and availability.

The pyridine is incorporated in the bath either as such, or in the form of a derivative which is capable of liberating pyridine under the conditions present in amounts sufficient to act as a catalyst to promote the cellulose esterification.

Thus, there may also be employed as a bath additive, a derivative of pyridine which possesses surface activity. For example, there may be employed for this purpose, in accordance with the invention, a cation-active pyridine derivative such as steararnidomethylpyridinium chloride, which is sold commercially under the designation Zelan. It is known in the prior art to employ such cation-active products as softening agents in subsequent washing treatments of the finished textile, but the incorporation of 5 small amounts of these agents in the urea-phosphoric type compounds may be used. Examples of substitution products of pyridine which are suitable as additives include alkylpyridines, particularly lower alkylpyridines, such as, for example, the picolines (2-methyl, 3-rnethyl-, and 4- methyl-pyridine), ethylpyridines, such as 3-ethyl-, or 4- ethyl-pyridine, lutidine (2,6-dimethylpyridine) or collidine (2,4,6-trimethyl-pyridine). There may also be employed mixtures of pyridine and/ or alkylpyridines, such as for example bone oil, which includes pyridine and other pyridine bases in admixture.

The amount of the pyridine-containing material to be added to the bath will vary according to the function which it is to perform, but will generally be in the range of about 0.5% to about 2.0% based upon the total weight of the urea or other nitrogen base and the phosphoric acid employed.

There may also be added to the flameproofing bath auxiliary solvents which are water-miscible, such as, for example, the ethylene glycol monoalkyl ethers. Examples thereof include ethylene glycol monoethyl ether, ethylene glycol monopropylether, and ethylene glycol monobutyl ether. These solvents facilitate penetration of the reaction into the interstices of the fabric.

There may also be advantageously added to the treating bath, surface-active substances, particularly those which are anion-active or which are nonionic. Especially suitable are alkali metal salts of alkyl aryl sulfonic acids, in which the alkyl radical has a carbon content from about 8 to about 18 carbon atoms. Thus, for example, there may be used in this connection a sodium alkyl benzene sulfonate in which the average chain length of the alkyl radical is 12 carbon atoms.

In accordance with one aspect of the invention, the urea or similar nitrogen base and the phosphoric acid, e.g. 100 parts urea to 50 parts of phosphoric acid by weight, are mixed and heated to a temperature between about 260 F. and about 400 F. to form a urea-phosphoric acid composition by reaction between the base and the acid. The mixture, which may be a molten mass, depending upon the temperature, is allowed to cool and is dissolved in water. There is added to the water solution, a small amount of pyridine, or a derivative of pyridine, together with an auxiliary solvent and a surfaceactive agent, as described previously.

Typical urea-phosphoric acid bath compositions of the foregoing type are disclosed in the following formulations, which are to be regarded as illustrative, but not as limiting:

Example 1 Gms. Urea-phosphoric acid 25.0 Pyridine base mixture (bone oil) 0.2 Ethylene glycol monoethyl ether 7.0 Sodium alkyl aryl sulfonate 0.2 Water 65.0

Total 97.4

Example 2 Urea-phosphoric acid 33.0 Pyridine 0.1 Ethylene glycol monobutyl ether 9.2 Sodium alkyl aryl sulfonate 0.1 Water 70.0

Total 112.4

Example 3 Urea-phosphoric acid 20.0 Methyland ethyl-pyridine mixture (equal weights of each) 0.4 Ethylene glycolmonoethyl ether 0.6 Sodium alkyl aryl sulfonate 0.3 Water 60.0

Total 81.3

4 Example 4 Urea-phosphoric acid 15.1 Methylpyridine 0.1 Ethylene glycol monopropyl ether 4.0 Potassium alkyl aryl sulfonate 0.3 Water 70.0

Total 89.4

In accordance with a preferred embodiment of the invention, there is employed a fiameproofing composition which comprises a reaction product of urea-formaldehyde and phosphoric acid. In the preparation of this composition, the urea-formaldehyde reaction product is first dissolved in warm water, with stirring. It is essential that the water temperature be carefully maintained within particular limits, namely between about 90 F. and about 120 F. Above 120 F. there is a tendency for a precipitate to be formed, causing turbidity which is undesirable. For this reason also, it is desirable that the solution be freshly prepared each time a batch is made, since the tendency toward precipitation manifests itself when the solution stands more than about 12 hours.

A form of urea-formaldehyde reaction product which has proved advantageous is that available commercially under the designation Pyroset DO, sold by E. I. du Pont de Nemours and Company, and which is a mixture of 77-88% urea-formaldehyde and 1218% melamine, by

weight, forming a white powder.

The preparation of a composition utilizing this product and phosphoric acid is described in the following example:

Water 312.0

The 120 lbs. of Pyroset DO ismixed with 40 lbs. of water to form a slurry, employing a variable speed rotary propeller blade mixer. The temperature of the water is maintained between 90 and 120 F. The mixing is continued until a clear, homogeneous solution is obtained. This takes about one hour, and depends upon the water temperature. There are then added to the clear solution, at intervals, 266 lbs. of water and 48 lbs. of phosphoric acid, while controlling the temperature to remain within the -l20 F. range. The reaction is exothermic, and additional water may be added in small amounts intermittently to control temperature. The amount of orthophosphoric acid used is approximately 40% by weight of the Pyroset DO. During the I mixing of the Pyroset DO with water there is prepared a separate solution of the sodium alkyl aryl sulfonate, the function of which is to swell the fibers and allow better penetration, by dissolving 1.92 lbs. of the sulfonate in 3 lbs. of water. There is also prepared a solution of 3 lbs. of Zelan (stearamidomethyl pyridinium chloride) in 3 lbs. of water. The solutions of the alkyl aryl sulfonate and of the Zelan are gradually added to the ureaformaldehydephosphoric acid mixture, maintaining the temperature between 90 and F., with constant stirring. The complete composition has a maximum usable life or about 13 hours, and must be maintained within the stated temperatures, avoiding turbidity. The composition has a pH value between 5.4 and 6.3.

The method of applying the flameproofing compositions of the invention to fabrics, such as, for example, cotton textiles, involves passing the fabric through the solution a sufficient number of times to achieve saturation. The fabric is then passed through squeeze rolls under 500 to 2000 lbs. pressure to assure uniformity of penetration and removal of excess composition. The

5. pressure varies according to the weight and construction of the fabric. The saturated fabric is then dried in an oven for 2 to minutes at a temperature of 200 to 250 C. If desired, the fabric may again be saturated with flameproofing composition and dried as before. The material is then cured at about 330 to 400 F. for about 2 to 12 minutes. The material may then be subjected to a softening operation employing conventional softening agents, and dried and stretched.

Thus, in applying the compositions of Examples l-4, clean cotton fabric is immersed in the solution until thoroughly and uniformly saturated, and then removed and excess solution removed by squeezing between rubber covered rolls, providing a wet pick-up of solution of about 75l00% by weight. The fabric is then dried at 200 F. and cured at about 325 F. for 3 minutes. The cured fabrics are washed and dried. The flameproofed fabrics thus prepared retain their original hand and feel and their tensile strength, as measured by at Scott tensile strength and elongation tester is substantially that of the untreated fabrics. In the vertical-Bunsen flame test the fabric samples showed no appreciable after-flaming, an afterglow of about 4 to 5 seconds, and a char length of about 3.2 inches.

The method of flameproofing with the preferred embodiment of the invention is illustrated by the following example:

Example 6 The flameproofing solution, prepared as in Example 5, is placed in a jacket dip tank where the temperature can be maintained within the critical limits of a maximum of 120 F. and preferably not below 90 F. The fabric, by the use of suitable rollers, is placed through the solution, dipping the necessary number of times so as to substantially saturate the fabric. The number of passes necessary to substantially saturate the fabric is dependent upon the structure and weight of the fabric being dipped. A fabric with loosely twisted fibers and of average light weight structure requires a lesser number of dips as compared with a fabric with tightly twisted fibers and of a heavy weight.

The saturated fabric is then passed through squeezing rollers set at a pressure of from a minimum of 500 pounds to a maximum of 2,000 pounds per square inch to secure uniformity throughout the fabric and the removal of excess solution. The pressure is dependent upon the weight and construction of the fabric. The lighter the fabric, and the looser the weave, the less pressure is required. The pressure is regulated so as to cause a retention of solution of 75% of the weight of the fabric dry 'per unit area.

The fabric is then passed into an oven at a temperature of 200 F. to 250 F. until it is completely dried. For the average light weight cotton fabric the time required is from 2 to 5 minutes. For a fabric such as No. 1 Army Duck, the time will be proportionately longer. When the water has been completely evaporated from the fabric, there should be no more than of the weight of the dry solution retained nor less than 12% by weight.

In the case of tightly woven heavy fabrics, it may be necessary to redip in the solution in the same manner as above to attain the desired solution retention.

The retention of solution is dependent upon: (,1) The hardness of the twist of the yarn in forming of the fabrics; (2) speed with which the fabric is passed through the immersion bath; (3) the pressure exerted by the squeeze rollers; (4) the weight of the fabric.

When the solution pick up and drying are completed, the treated fabric is passed in to a curing oven at a temperature of 330 F. to 400 F. for a period of 1 /2 minutes to 3 minutes depending again on the structure of the fabric with the hard twisted heavier fabrics requiring a longer curing time. The treated fabric as it passed from the curing oven has a comparatively brittle finish and requires a softening operation to be usable. The softening operation is accomplished by passing the cured fabric into a 35% solution of a Wetting agent at a temperature of F. to F.

A white sateen fabric treated as described exhibited the following fire resistance characteristics:

FIRE RESISTANCE AFTER 20 WASHINGS Warp Direction Filling Direction After Char After Char Flame, Length, Flame, Length,

sec. inches sec. inches Avg. 0. 1 3. 8 0. 2 4. 0

The above test was conducted in accordance with the procedure outlined in Specification A.A.T.C.C. Method 34-1952.

The feel and texture of the original fabric were preserved, and there is no significant color change. The flameproofing is substantially wash-proof and even after 15 washings with a soap or detergent the flameproofing can be restored by Washing in an acid bath. Fabric drycleaned 50 times exhibits no loss of fiameproof properties.

I claim:

1. Method of flameproofing a cellulosic textile material which comprises the steps of applying to said cellulosic textile material an aqueous solution of the reaction product made by heating at a temperature between about 260 F. and about 400 F. about 2 to about 6 mols of an organic nitrogen base selected from the group consisting of urea, melamine, guanidine and dicyandia-rnide and about 1 mol of an acid of phosphorous selected from the group consisting of orthophosphoric, metaphosphoric, pyrophosphoric, orthophosphorous, pyrophosphorous and polyphosphoric acid, adding to said aqueous solution of the reaction product from about 0.5% to about 2.0% based upon the total weight of the organic nitrogen base and the acid of phosphorous, of a :heterocyclic nitrogen compound selected from the group consisting of pyridine, lower alkyl pyridines, a cation-active quaternary ammonium derivative of pyridine which liberates pyridine under the method conditions and quinoline, drying and curing said treated textile material by heating at a temperature between about 330 F. and about 400 F. for a period of about 2 to about 12 minutes.

2. A cellulosic textile flameproofed by the method of claim 1.

3. Method of flameproofing a cellulosic textile material which comprises the steps of applying to said cellulosic textile material an aqueous solution of the reaction product made by heating at a temperature between about 260 F. and about 400 F. about 2 to 6 mols of urea and about 1 mol of orthophosphoric acid, adding to said aqueous solution of the reaction product from about 0.5% to about 2.0% of pyridine based upon the total weight of the urea and phosphoric acid, drying, and curing said treated textile material by heating at a temperature between about 330 F. and about 400 F. for a period of about 2 to about 12 minutes.

4. A cellulosic textile flameproofed by the method of claim 3.

(References on following page) References Cited by the Examiner UNITED STATES PATENTS Dearing 260-69 Reynolds et al. 8-1161 Hearn 106-15 Schirm 8-1163 Leatherman 10615 Burke 8116.3 Thomas et al. 8-120 Rohner et a1. 260-69 X Pollak 117-137 Ford et a1. 8-116.2 Ford et a1. 8-1163 Ford et a1. 8-1162 Edelstein 8-1162 X Garner et a1. 260-69 Reeves et a1.

' FOREIGN PATENTS 8 OTHER REFERENCES Davis et al., Journal of the Textile Institute, Transactions, Dec. 1949, pages T839-T854.

Hackhs Chemical Dictionary, 3rd Edition, 1944, page 178.

Handbook of Solvents, Scheflan et al., 1953, pages 415-418.

Nuessle, Textile Research Journal, Jan. 1956, pages 32-39.

A. Bernthsen et al., Textbook of Organic Chemistry, 1931, pages 571-573.

Worden, Edward C., Technology of Cellulose Esters, 1916, vol. 8, page 2948.

Worden, Edward C., Technology of Cellulose Ethers, 1933, vol. 1, page 278, vol. 2, pages 709 and 987, vol. 3, pages 1235 and 1236.

NORMAN G. TORCHIN, Primary Examiner.

20 H. WOLMAN, Assistant Examiner. 

1. METHOD OF FLAMEPROOFING A CELLULOSIC TEXTILE MATERIAL WHICH COMPRISES THE STEPS OF APPLYING TO SAID CELLULOSIC TEXTILE MATERIAL AN AQUEOUS SOLUTION OF THE REACTION PRODUCT MADE BY HEATING AT A TEMPERATURE BETWEEN ABOUT 260*F. AND ABOUT 400*F. ABOUT 2 TO ABOUT 6 MOLS OF AN ORGANIC NITROGEN BASE SELECTED FROM THE GROUP CONSISTING OF UREA, MELAMINE, GUANIDINE AND DICYANDIAMIDE AND ABOUT 1 MOL OF AN ACID OFPHOSPHOROUS SELECTED FROM THE GROUP CONSISTING OF ORTHOPHOSPHORIC, METAPHOSPHORIC, PYROPHOSPHORIC, ORTHOPHOSPHOROUS, PYROPHOSPHOROUS AND POLYPHOSPHORIC ACID, ADDING TO SAID AQUEOUS SOLUTION OF THE REACTION PRODUCT FROM ABOUT 0.5% TO ABOUT 2.0% BASED UPON THE TOTAL WEIGHT OF THE ORGANIC NITROGEN HAVE AND THE ACID OF PHOSPOROUS, OF A HETEROCYCLIC NITROGEN COMPOUND SELECTED FROM THE GROUP CONSISTING OF PYRIDINE, LOWER ALKYL PYRIDINES, A CATION-ACTIVE QUATERNARY AMMONIUM DERIVATIVE OF PYRIDINE WHICH LIBERATES PYRIDINE UNDER THE METHOD CONDITIONS AND QUINOLINE, DRYING AND CURING SAID TREATED TEXTILE MATERIAL BY HEATING AT A TEMPERATURE BETWEEN ABOUT 330*F. AND ABOUT 400*F. FOR A PERIOD OF ABOUT 2 TO ABOUT 12 MINUTES. 